As others have said I think you will probably want to reflect on this a bit more.
Having been a lodger in a similar position in the past and having had friends who have had lodgers in their houses both short term and long term my thoughts/advice is
First off before thinking about what rules you are going to have people live by think about how you will feel sharing your house with another person.
Will you resent them using your kitchen? Will you want to be in the same sitting room as them? Will you eat with them or allow them to cook separately? Will you give them their own fridge? Own cupboard? Will you provide basics - tea, coffee, milk etc or will they have to buy their own? Will you want to be with them at the weekends?
How do you feel about someone else having a key to your house and being able to come and go when they want with you having no idea or control? Would you be happy them being at home in the daytime whilst you are at work? What about if someone works night shifts? Will you resent them if you come home from work tired and they are sat watching Pointless?
Then think about how you are going to get the lodgers - best source is people you know/ friends of friends etc: can you advertise at your workplace, do you know people locally looking for housing? Having a personal connection with the lodger will lead to a more fulfilling relationship and may even lead to a friendship/ you wont resent them as much.
Think about realistically how appealing your bedroom would be. Who are the people who will want to have a room in a house? Are you near a university or hospital or other large employer? Where are in relation to the town centre/do you have parking available? You state that you live in an inexpensive area - why would people pay for your bedroom if they could get their own house/flat for little more? What can you offer that a room in a shared house doesnt?
As others have said I think you are being optimistic to rent out two rooms - unless you are in a city centre location where there is strong demand the single will be hard to let. The double will be the most attractive and give you the most privacy as the lodger will have more scope to spend time in their room.
Having a large double room available sounds great - furnish it minimally with basics and it should go fine. Go for the basic wood/ minimalist 'Ikea' look and it should be very appealing.
If you are not letting out the single I would create a study/dressing/living room for yourself so that you have somewhere for yourself.
Think finanically - you will have increased expenses including probably having to buy some new furniture - maybe a new mattress/bed etc. You will also have increased general costs - electricity, gas, general wear and tear etc.
And bank on the fact that your room may be empty for two - three months a year. In many cases the lodgers will only be for a short term - the value of lodgings is that they are short term for people who dont want a minimum six month contract, eg someone who needs accommodation whilst they find somewhere to live. If they are going to stay in the area longer term they will want to get their own place if as you say its not expensive.
And make sure you get a deposit, ideally one months rent but even if only an amount, say £100, so that people are committed to you and will want to get their money back.
And wor d your advert carefully - describe you age and temperment - ie 'Quiet 30s single woman professional seeks similar as lodger' etc. That way you should get someone suitable and the expectations will be implicit rather than you having to give them a page of rules and reguilations.